The total change in internal energy would simply be calculated using the formula:
ΔU = -P (V2 – V1) + ΔH
where ΔU is the change in internal energy; P is constant pressure = 30 atm = 3,039,750 Pa; V2 is final volume = 2 L = 0.002 m^3; V1 is initial volume = 7.20 L = 0.0072 m^3; while ΔH is the heat = -74,400 J (heat released so negative)
Therefore:
ΔU =-3,039,750 Pa * (0.002 m^3 - 0.0072 m^3) + (- 74,400 J)
ΔU = - 58,593.3 J = - 58.6 kJ
